1. Field of the Invention
The present invention provides a crystal resonator having vibrating regions in which the positive and negative directions of the X-axis differ from each other within a surface thereof, and a crystal oscillator including the crystal resonator.
2. Description of Related Art
Crystal resonators used in electronic components such as an oscillating circuit have frequency temperature characteristics in which the oscillating frequency changes in accordance with the temperature. These frequency temperature characteristics differ in every crystal resonator depending on the cutting angle, thickness, and the like of a crystal wafer constituting the crystal resonator.
Therefore, various innovations have been devised to obtain a stable frequency output regardless of the ambient temperature. For example, the following has been proposed: constituting a first crystal resonator and a second crystal resonator by forming two groups of excitation electrodes that create a pair with each other on a common crystal wafer, calculating the difference in output between the first crystal resonator and the second crystal resonator, and utilizing this output. The first crystal resonator and the second crystal resonator constituted by a common crystal wafer as described above are affected in the same way by the surrounding temperature, and thus the influence of the surrounding temperature is minimized in the frequency output of the difference. However, calculating the difference in frequency as described above renders the constitution of the apparatus complex.
If a plurality of vibrating regions are formed on the same crystal wafer, it is necessary to constitute the crystal wafer so that the influence of one vibrating region on the other vibrating region(s) is minimized. For example, in Japanese Patent Application Laid-Open (JP-A) No. 2007-108170, a recess is formed on the crystal wafer, and the vibrating regions are partitioned from each other by the recess. However, it is difficult to solve the problem of obtaining a simple oscillating apparatus with a crystal wafer having such a constitution because the regions partitioned by the recess are both AT cut. Japanese Patent Application Laid-Open (JP-A) No. 2003-69374 discloses a technology in which a crystal wafer is twinned by irradiating a laser on the periphery of an AT-cut crystal wafer to invert the positive/negative of the crystallographic axis. However, the periphery which is irradiated by the laser is constituted as a region that supports a center portion, which is a region that is AT cut, without vibrating, and thus this technology cannot solve the above-described problem.
Some crystal oscillators are known to be used as temperature sensors using a thermistor or the like. The oscillation output is controlled based on the temperature detected by the temperature sensor, but a crystal oscillator that can achieve stable oscillation with a simpler constitution is desired.